In electric arc reduction furnaces, the electrodes an essential component, through which electric energy is conducted, triggering the electric arc in the lower part and producing a temperature sufficient that chemical reduction may occur in the furnace.
The electric current is introduced to the electrode by means of the contact plates or plows, generally more than one, that are pressed against the electrode itself by means of pressure rings or crowns. The plates are normally made of copper and the pressure rings may be of copper or another material and both are usually strongly cooled with water.
Usually, the electrodes are made of carbon in its different forms. They are consumed in the arc area as the reaction is produced in the furnace and they are replaced through the upper part of the column. They may be classified as prebakes, when they have been prepared already baked and machined outside the reduction furnace, or they may be self-baked in the furnace itself, in which case the raw material to be baked will be introduced in the upper part of the column and will bake as it descends therealong.
The paste before baking is known as green paste and is mixture of different types of carbons limed at high temperatures with pitches which act as binders. This green paste is usually supplied as briquettes or cylinders with a smaller diameter than that of the electrode itself which is to be introduced through the upper part of the column. As the temperature increases, the softening point of the paste is reached, from which the paste becomes liquid and tends to fill all the gaps and uniformly be distributed in a horizontal section of the electrode column.
To permit this baking, the electrode column should be provided with a metal hoop, generally cylindrical with a specific diameter depending on the furnace type. The purpose of this hoop is to facilitate the electrode formation acting as a container during the phase changes of the carbon paste is introduced inside it.
Although the object of the invention may be applied to any type of electric conduction involving a change of phase in the raw material of an electrode, the specific application of this invention has been made for carbon paste electrodes used in submerged electric arc furnaces for the production of ferroalloys. Another application would be in the manufacture of the electrodes themselves when they are baked outside the furnace or in any other type of production such as vats for the manufacture of aluminum.
The resistance values of the paste on passing the current may vary considerably, depending on whether it is in a green state with many gaps between the parts or if it is liquefied and then baked. In all these processes, volatile gases are produced and cokification of the pitch occurs, so that when the corresponding temperature is reached, the electrode is a highly conductive carbon mass with a shape determined by the hoop itself.
All these transformations are of maximum importance to obtain a good baked electrode satisfying its function in the furnace without problems. However, they are produced along the column which has a variable length between three and ten meters and in an area where there is no access for observing or studying the baking of the paste. Several studies have been made by introducing thermocouples along the column and from whose temperature the baking state of the paste may be deduced. Mathematical models have also been made, starting from the Maxwell equations and the contour conditions of the electrode itself which indicate temperature values and even intensity along the electrode. This gives an indication as to what actually occurs inside the column, but in the daily use of furnaces it is impossible for these methods to indicate what is being produced at each moment, so that it is impossible to prevent problems of maladjustment or furnace destabilization and of the electrode itself.
Regarding the state of the art, it is known that the electrode has a core of metal, amorphous or of another type of material. Two patents may be mentioned having a graphite core, Spanish Patent number 9102414/5 issued to Ferroatlxc3xa1ntica, directed to IMPROVEMENTS ON THE CONTINUOUS MANUFACTURING PROCESS OF IMPURITY FREE ELECTRODES AND IRON FOR ELECTRIC ARC FURNACES and U.S. Pat. No. 4,575,856 issued to J. A. Persson directed to IRON FREE SELF BAKING ELECTRODE.
It is therefore an object of the invention to provide an apparatus and method to enable determination at any moment of the condition of the paste inside the column and to detect any irregularity in paste uniformity, density or compacting that may later give problems in the electrode and in the furnace operation as a result.
To achieve this and other objects, the invention is directed to a low and known impedance conducting element introduced in the electrode center, such as the aforementioned graphite, and also copper, iron, aluminum or other good metal conductor. The conductor component will have a diameter based on the electrode diameter in a proportion generally calculated based on previous experiences, and which may be introduced through the upper part of the column, lowering through the electrode center therealong until it is melted in the lower part of the electrode and once baking of the paste has been produced, which takes place at about 500xc2x0 C. The higher the melting point, more information may be obtained on the column situation. It is important that this conducting component does not contaminate the product being manufactured in the furnace.
Through this conducting component, a low power electric current is introduced having known intensity and frequency. A response signal is collected through the contact plates, closing the circuit conveying the signal to a means for analysis.
In this way, the current generated at a determined frequency and voltage will be introduced in the upper part of the electrode through the aforementioned central conductor component and will be transmitted through the central conductor until it reaches the plate, crossing the carbon paste, and from there to the copper pipe, where it closes a circuit in the equipment itself.
When this circuit is introduced in a mathematical electrode model, it can be proven that the current produced always follows the route of minimum impedance. For this reason, depending on the frequency at which the current is introduced, it will transmit more or less through the length of the central conductor and will go to the hoop or the external surface of the electrode at different heights. Through the equipment, we may know the impedance values at each one of the different frequencies and collect the signal in each one of the plates and therefore, in the entire horizontal section of the electrode. All this data is collected in a digital processor connected to a computer analyzing the different signals and shows values indicating the internal situation of the electrode.
Further information concerning the features of the invention can be obtained from the attached drawing, disclosing schematically an example representing the preferred and essential details of the invention.